Today Operating systems are often creating system files to accelerate directory operations:

MacOSX: ‘.DS_Store’
Windows: ‘Thumbs.db’
KDE: ‘.directory’
….

To avoid that these files mess up your repository, create inside the 'hook' directory a file named: 'pre-commit' (beside a the example file ‘pre-commit.tmpl’).
It is very important to make sure that the script has execution rights ( chmod a+x pre-commit )